This invention relates in general to internal drum scanner assemblies and laser imaging systems incorporating such scanner assemblies. In particular, the present invention relates to a baffle for extinguishing second surface reflections in an optical scanner assembly having a lens located between the scanner and photosensitive media.
Laser imaging systems are commonly used to produce photographic images from digital image data generated by magnetic resonance (MR), computed tomography (CT) or other types of medical image scanners. Systems of this type typically include a continuous tone laser imager for exposing the image on photosensitive film, a film processor for developing the film, and control subsystems for coordinating the operation of the laser imager and the film processor.
The digital image data is a sequence of digital image values representative of the scanned image. Image processing electronics within the control subsystem processes the image data values to generate a sequence of digital laser drive values (i.e., exposure values), which are input to a laser scanner. The laser scanner is responsive to the digital laser drive values for scanning across the photosensitive film in a raster pattern for exposing the image on the film.
The continuous-tone images used in the medical imaging field have very stringent image-quality requirements. A laser imager printing onto transparency film exposes an image in a raster format, the line spacing of which must be controlled to better than one micrometer. In addition, the image must be uniformly exposed such that the observer cannot notice any artifacts. In the case of medical imaging, the observers are professional image analysts (e.g., radiologists).
Film exposure systems are used to provide exposure of the image on photosensitive film. Known film exposure systems include a linear translation system and a laser or optical scanning system. The laser scanning system includes a laser scanner with unique optical configurations (i.e., lenses and mirrors) for exposure of the image onto the film. The linear translation system provides for movement of the laser scanning system in a direction perpendicular to the scanning direction, such that a full image may be scanned on a piece of photosensitive film.
U.S. Pat. No. 5,883,658, issued Mar. 16, 1999, inventors Schubert et al. discloses an optical scanner assembly for exposing an image on a photosensitive media. The media is positioned on the internal surface of a drum platen. The optical scanner assembly includes a laser assembly for producing a laser beam representative of the image to be exposed on the photosensitive media, a scanner, and a long, flexible lens curved to the semi-circular shape of the media positioned on the internal surface of the drum platen, the lens being positioned between the scanner and the film. This scanner operates to scan the laser beam across the media in an image-wide pattern. The lens is plano-convex with the convex side facing the film. The lens is tilted from a perpendicular position relative to the laser beam axis.
It has been found that laser beam reflections from the highly divergent surfaces of the convex lens propagate backwards to the media on the opposite side causing undesirable exposures and creating visually objectionable image artifacts in the media. There is thus a need to eliminate these undesirable reflections.
According to the present invention, there is provided a solution to the problems discussed above.
According to a feature of the present invention, there is provided an optical scanner assembly for exposing an image on photosensitive media positioned on the internal surface of a drum platen, the assembly comprising: a laser assembly for producing a laser beam representative of the image to be exposed on photosensitive media; a laser beam scanner positioned between said laser assembly and said media to scan said laser beam through the lens across the media in an image-wide pattern; and a baffle located between said scanner and said media for extinguishing laser beam reflections from said lens.
The invention has the following advantages.
1. Laser beam reflections in an internal drum laser scanner assembly are extinguished to eliminate undesirable exposures and visually objectionable image artifacts in exposed media.